Television display system

ABSTRACT

A television display system for a scanning electron microscope provides a spatially correlated area map display of X-ray events emitted from a specimen within one or more predetermined energy ranges as the specimen is scanned at standard television scanning rates by an electron beam. The X-ray area map display can be presented alone, or in combination with a conventional micrograph magnified image of the specimen. Provision is made for displaying X-ray events falling within different energy ranges in different colors on the area map television display to facilitate determining the distribution of selected elements within the specimen, and for color coding the distribution peaks on an associated X-ray energy distribution television display to facilitate correlation with the elements displayed in the area map display.

United States P Walsh et al.

atent {ii-ii 3,812,288

[ May21, 1974 TELEVISION DISPLAY SYSTEM 3,648,270 3/1972 Metz et al..... 340/324 AD Inventors: Charles J Walsh, Deerfield; Morris 3,678,498 7/1972 Nagamatsu err a1. 340/324 AD W. Barnhart, Buffalo Grove, both of 111. Primary Exammer-Howard W. Britton Assistant Examiner-Michael A. Masinick [73] Ass1gnee: Edax International Inc., Prairie Attorney, Agent, or F j M wetzei View, 111.

1 Appl 308522 A television display system for a scanning electron microscope provides a spatially correlated area map dis- [52] US. Cl 178/63, 178/DlG. 1, l78/DlG. 5, play of X-ray events emitted from a specimen within 250/31 1, 250/399 one or more predetermined energy ranges as the spec- [51] Int. Cl. H04n 7/18 imen is scanned at standard television scanning rates [58] Field of Search 178/68, 7.2, DIG. 5, D16 1; by an electron beam. The X-ray area map display can 340/324 AD; 250/307, 310, 311, 397, 399 be presented alone, or in combination with a conventional micrograph magnified image of the specimen. [56] References Cited Provision is made for displaying X-ray events falling UNITED STATES PATENTS within different energy ranges in different colors on the area map television display to facilitate determin- 7 ing the distribution of selected elements within the 3:432.66l 3/1969 Hodgkinson.... 250/833 Specimen, and for Color Coding the distribution Peaks 3,675,232 7/1972 sn 34 4 AD on an associated X-ray energy distribution television 3,614,311 /1971 Fujiyasu et a1 ,1 178/68 display to facilitate correlation with the elements dis- 2,996,576 8/1961 played in the area map display. 3,229,089 1/1966 i 3,205,344 9/1965 Taylor et a1. 235/154 11 Claims, 9 Drawing Figures Analog Energy Television &- 32%: To Digital Distributing Display Converter Analyzer Generator 55M 1 1 56 Display 10 i f Video 11 35 DDizlpg Multiplexer Proces'sing 14 Timer 44 45 Circuits Television F Monitor 12 Single Single 57 Channel Channel 2 X Window Window 53 1e *1 2 7 24 l i 54 9 X] l Scanning I Telev sion Circuits r Color Monitor '3 N'trogen Modulator 1 Dewar l Energy g 55 Distribution Generator 3 58 MHZ 46 47 DISD y 3.58 M Hz.

CQIOF C0101" 0501mm? Oscillator 52 51w Micrograph i i o oX-Ray Map C0101" Processing 1 Composit? Modulator Circuits x 1 TELEVISION DISPLAY, SYSTEM BACKGROUND OF THE INVENTION This invention pertains to video display systems, and more particularly to a display system for a scanning electron microscope.

Scanning type electron microscope (SEM) systems, wherein a narrow electron beam is caused to periodically scan across the surface of a specimen, have come into wide use for the examination of rough specimens, such as a fracture or a particle in a substrate. In such systems a detector, mounted adjacent the specimen, detects the incidence of secondary electrons as the specimen is scanned to develop a video signal indicative of the electron density of the specimen. This video signal, after amplification, is utilized to intensitymodulate the electron beam of a cathode-ray tube. When this electron beam is caused to scan in synchronism with the electron beam of the SEM, an output display is formed on the face of the cathode-ray tube showing the threedimensional surface features of the specimen with magnifications typically from to 20,000 times.

The usefulness of a SEM system is greatly enhanced if an elemental analysis can be made of the specimen at the same time the specimen is being scanned. This is accomplished by detecting and measuring the X-rays emitted from the specimen as it is scanned. The energy level of these X-rays is proportional to the atomic number of the element emitting the X-rays, and thus can be used to unequivocably identify the element. Furthermore, the relative number of X-rays of various energies can be used to calculate the relative abundance of the different elements in the specimen. Energy-dispersive analysis systems commonly used in conjunction with SEM systems for elemental analysis employ a highly purified silicon diode detector for developing current pulses proportional to the energy level of the X-ray events. After amplification, these pulses are sorted and tabulated according to their energy level in a multichannel energy distribution analyzer to ascertain the complete energy spectrum of thespecimen. All or portions of this spectrum can then be displayed as a histogram on a cathode-ray tube, or can be printed-out by means of a teletype terminal or data plotter.

Energy-dispersive analysis systems can also be equipped to single out specific energy level pulses, and hence specific elements. This is accomplished by means of a single channel window circuit which is set to recognize only signals within a predetermined energy range, or window, and to ignore all others. All X-ray events falling within this window can be separately processed and tabulated, allowing the presence of a selected element to be accurately determined.

One particularly useful application for the single channel window is to provide an area map of the selected element on the output display of the SEM system. This may be done by intensity-modulating the electron beam of the cathode-ray display tube, either so that only the selected element will be displayed, or so that the selected element will be made to stand out in some manner from the rest of the display.

Unfortunately, there is an inherent delay of from 20 to 100 microseconds in energy-dispersive analysis sys terns in detecting and identifying the X-ray emissions fnn the specimen. In the case of a slow scan SEM system this delay presents no problem, since the horizon tal sweep is very slow, typically in the order of milliseconds, and the spatial resolution error of the 100 microsecond delay is only 0.1 percent. However, in the case of television-type SEM system displays, the X-ray detection delay has heretofore made X-ray mapping impossible. This is because in systems of this type the horizontal sweep is typically only 63.5 microseconds, so that the horizontal spatial error resulting from the X-ray detection delay ranges from 30 percent to percent. Since the actual delay is variable, depending on the energy of the X-ray event, the X-ray area map of an element resulting from direct application of a sin gle-channel window output to the SEM system display is spatially distorted and of no practical value.

SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a new and improved display system for a scanning-type electron microscope wherein elemental identification from an energy-dispersive X-ray analysis system is displayed in spatial correlation to the micrographic output display of the microscope.

It is a more specific object of the present invention to provide a new and improved television display system for a scanning-type electron microscopewhich provides an elemental area map with reduced horizontal spatial error. t

The usefulness of an energy-dispersive X-ray analysis system is further enhanced by being able to identify and display the location of two or more elements at one time. While it is possible to provide more than one single-channel window to identify multiple elements, heretofore no satisfactory means has been known for differentiating between different elements in the SEM system display.

v Accordingly, it is another general object of the present invention to provide a display system for a scanning-type electron microscope which provides a simultaneous X-ray area-map of multiple elements.

It is another more specific object of the present invention to provide a television display system for a scanning-type electron microscope which provides a means for correlating elements displayed on a multipleelement area map display with those represented on a simultaneous energy histogram display.

It is another more specific object of the present invention to provide a television display system fora scanning-type electron microscope wherein individual ones of multiple elements are uniquely identified and displayed in spatial correlation to the micrograph output display of the microscope.

Accordingly, the invention is directed to a display system for a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam. The system comprises a detector for detecting the X-ray events and producing output pulses indicative of the energy level thereof, and means for converting at least some of the output pulses to energy indicaincludes a television monitor having a viewing screen scanned in synchronism with-the specimen, and means are provided for applying the display pulses to the television monitor to obtain a spatially correlated display of the X-ray events.

The invention is further directed, in a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, to a display system comprising a detector for detecting the X-ray events and producing output pulses indicative of the energy level thereof, and means for converting at least some of the output pulses to energy-indicative information signals, the information signals following their associated events by random unpredictable time intervals. The display system further comprises a first single-channel window circuit for analyzing the information signals to produce a first control effect when one of the signals falls within limits corresponding to a first predetermined energy range, and a second single-channel window circuit for analyzing the information signal to produce a second control effect when one of the signals falls within limits corresponding to a second predetermined energy range. Further included are means including a timer responsive to the first control effect for producing a first display pulse and responsive to said second control pulse for producing a second display pulse, each of the pulses being provided after a predetermined delay period following the X-ray event associated with the respective control effect. The display system further comprises a television monitor having a viewing screen scanned in synchronism with the specimen, and means for applying the first and second display pulses to the television monitor to obtain a spatially correlated display of the X-ray events having energy levels within the first and second predetermined energy ranges.

The present invention is further directed, in a scanning electronmicroscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, to a display system comprising a detector for detecting the X-ray events and producing output pulses indicative of the energy level thereof, and means for converting at least some of the output pulses to energy-indicative information signals, the information signals following their associated events by random unpredictable time intervals. The display system further comprises a color television monitor, and an energy distribution analyzer for developing on the television monitor from the information signals a histogram-type display of the energy levels of the X-ray events versus their cumulative occurrence over a period of time. Also included are a first single channel window for analyzing the information signals to generate a first control effect when the signals fall within limits corresponding to a first predetermined energy range, and means for varying the color of the histogram display to identify that portion of the display falling within the first predetermined energy range.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is a simplified functional block diagram of a scanning-type electron microscope television display system constructed in accordance with the invention to present a spatially correlated X-ray area map;

FIG. 2 is a spectral histogram of the energy levels of X-ray events helpful in understanding the operation of the display system of FIG. 1;

FIG. 3 is a vertically expanded depiction of a television scanning sequence helpful in understanding the operation of the display system of FIG. 1;

FIG. 4 is a vertically expanded depiction of another television scanning sequence helpful in understanding the operation of the display system of FIG. 1;

FIG. 5 depicts an SEM system micrographic output display helpful in understanding the operation of the display system of FIG. 1;

FIG. 6 depicts an elemental X-ray area map helpful in understanding the operation of the display system of FIG. 1;

FIG. 7 is a simplified functional block diagram of a scanning-type electron microscope display system constructed in accordance with the invention to simultaneously present X-ray area maps for two different elements;

FIG. 8 depicts a simultaneous elemental X-ray area map display for two different elements helpful in understanding the operation of the display system of FIG. 7; and

FIG. 9 is a spectral histogram of the energy levels of X-ray events helpful in understanding the operation of the display system of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the display system of the invention is shown in conjunction with a scanning-type electron microscope 10 which may be entirely conventional in design and operation. The microscope may include an electron gun 11, an electro-magnetic condensing lens 12, and an electromagnetic objective lens I3 for establishing and focusing an electron beam 14 onto the surface of a specimen 15. Because the scanning electron microscope is intended primarily for high resolution imaging, the electron beam is of relatively low intensity, typically in the order of IO amperes, to obtain the smallest possible contact point with the specimen. As mentioned previously, the specimen for this type of microscope will ordinarily have a rough surface and may consist of a plurality of tiny particles to be individually analyzed.

The electron beam 14 is caused to scan specimen by means of an electromagnetic scanning coil M. This scanning action may be two dimensional and like that of a television system wherein a relatively fast horizontal scan is utilized in conjunction with a much slower vertical scan. While the scanning rate is to some extent a matter of choice, in the present system it is purposely selected to be identical to the present United States standard, namely a 15,750 Hz line scanning rate and a 60 Hz field scanning rate. This permits conventional television monitors to be used, singly or in parallel, to display the output of the microscope and permits direct interface with other types of video equipment. Scanning coil 16 is driven by scanning circuits 17, which may include both horizontal and vertical circuits for establishing the necessary deflection currents in coil 16. These circuits are synchronized by means of a sync generator 18, which also has an output for synchronizing associated output display monitors.

As the electron beam scans specimen low energy secondary electrons are given off at a rate dependent upon the electron density of the specimen at the incident point of the beam. These electrons are detected by a detector 19, whichdevelops an output signal indicative of the electron density. This signal is applied to a high gain amplifier wherein it is amplified to a level suitable for application to video processing circuits 21. The synchronizing output signals from sync generator 18 are combined with the amplied detector output signal from amplifier 20 by video processing circuits 21 to form a composite television signal. This signal may be applied to one or more conventional television monitors 22 to obtain an output display showing the threedimensional surface features of the specimen as they would appear to the human eye at magnifications of from 20 to over 20,000 times.

Electron microscope 10 also has associated with it an X-ray energy-dispersive analysis system for analyzing the elemental composition of specimen 15. Data for this system is obtained by means of X-ray detector 23 positioned adjacent to the specimen. This detector may consist of a lithium-drifted silicon semiconductor, which when appropriately biased develops a charge proportional to the energy of the incident X-ray. This charge is integrated into a current pulse by a field effect transistor F ET) preamplifier. The silicon detector and its FET preamplifier are cooled with liquid nitrogen from an adjacent dewar 24 to stabilize the detector and to reduce the dark current (noise).

The signal from the preamplifier is amplified in a linear amplifier 25. The gain of this amplifier is variable but stable over extended time periods, thereby providing a means of calibrating the system and accommodating variations in detector efficiency. The amplified cur rent pulses from amplifier 25 are applied to a data gate 26, which allows only those pulses which the system is prepared to analyze to enter the system. That is, while the system is processing one or more previous pulses it may not have the capacity to process a closely following subsequent pulse, and therefore the subsequent pulse is ignored. Since the occurrence of X-ray events, and hence pulses, is random over any given period of time, this in no way affects the accuracy of the final elemental analysis.

The output pulses from data gate 26 are applied one at a time to an analog to digital converter 27 wherein each is converted to a binary number information signal indicative of its magnitude, and hence the energy level of the X-ray event. This information signal is applied to an energy distribution analyzer 28, wherein it is used in constructing an energy distribution spectrum of the specimen. Specifically, analyzer 28 contains a memory unit having a large number of locations each corresponding to a possible X-ray event energy level. A number stored in each such memory location indicates the number of X-ray events which have been received at that energy level. By adjusting the gain of amplifier 25, the binary number developed by converter 27 in response to an Xray event is made to correspond to the address of the memory location corresponding to the energy level of the event. Then, by utilizing the digital number from converter 27 as an address to locate a particular memory location, and up-dating the contents of that location by adding one count, it is possible to develop within the memory a complete energy spectrum for the specimen being analyzed. In practice, 400 or more such memory locations may be utilized in developing the final energy distribution spectrum. An output from analyzer 28 is also provided for controlling data gate 26.

If desired the information contained in the various memory locations can be read out into a teletypewriter or into a two-axis plotter to provide an indication of the energy spectrum of the specimen. However, it is often desirable to provide a real-time video display, and to this end a television display generator 29 and television monitor 30 are provided in conjunction with analyzer 28. Generator 29 systematically scans the memory locations of the analyzer at the line scanning rate of monitor 30, and in each case converts the stored counts of the memory locations to a proportional field intensification on the monitor. In practice this is facilitated by rotating the deflection yoke of monitor 30 by so that the slower 60 Hz field scan is horizontal and the faster 15,750 Hz line scan is vertical. This makes the entire 525 scanning lines of the US. standard, now displayed vertically, available for assignment to memory locations in analyzer 28. It will be appreciated that when each of these lines is extended up in proportion to the number or count stored in its corresponding memory location, a spectral display or histogram of the energy levels of the specimen results. A grid and additional alphanumeric information may be provided on the display by incorporating appropriate circuitry in generator 29.

It is often desirable to analyze a. certain energy level or range of energy levels to determine the presence of a particular element or group of elements. To this end, the X-ray analysis system of FIG. 11 includes a single channel window 31 which can be set to recognize and display one particular energy level, or centroid, or al tematively a range of energy levels. It accomplishes this by comparing an applied digital number with an internally stored digital number, and producing an output only when the numbers agree or are within the selected range. The stored number and the permissible range can be set by means of switches, or can be externally selected and retained in a portion of the memory of analyzer 28.

The input to window 31 is alternately switched between the output of analog to digital converter 27 and the read-out address output of television display generator 29 by means of a multiplexer 352. It will be recalled that analyzer 28 periodically scans the memory loca tions of its core storage unit for the: purpose of forming a spectral display. In so doing, it periodically generates addresses of these memory locations, and it is these addresses that are applied one at a time by multiplexer 32 to window 31 during one portion of its operating cycle. If the addresses, which correspond to discrete energy levels, fall within the range of window 31 an output pulse is produced. This pulse is utilized by analyzer 28 to enhance or brighten the video signal generated by display generator 29 so that the selected window will appear as a brightened area to the operator. it can also be used for statistical purposes, as for example, determining the total number of pulses within the window.

The histogram-type energy spectrum display produced on monitor 30 is shown in FIG. 2. Energy levels appear on the horizontal scale (10 electron volts per channel) and total events (10,000 per division) appear on the vertical scale. The window is shown as extending over and brightening an energy peak 33. A grid 34 is provided for operator convenience and an alphanumeric readout of the window centroid and display scale factors is provided at the top. In this case the window is centered at 4,510 electron volts, an energy level cor responding to the element titanium.

During the other portion of its operating cycle, multi' plexer 32 applies the digital output signals from converter 27, representing energy-levels of occurring X-ray events, to single channel window 31, wherein they are compared with the internally stored number to determine whether the events fall within the window limits. If they do, an output pulse is produced by window 31 for the purpose of producing an X-ray area map indicating the spatial distribution of the selected element, in this case titanium, on the SEM system display monitor 22.

However, it will be recalled that the processing time between the actual X-ray event and the completion of the window analysis is relatively long, in the order of 20 to I00 microseconds, so that the output pulse of window 31, if applied directly to monitor 22, would result in a large horizontal spatial error. Therefore, and in accordance with one aspect of the invention, a display delay timer 35 is provided for delaying the display of the X-ray event for a predetermined period of time equal to an integral multiple of the duration of one line scanning period. Specifically, delay timer 35 is triggered by the leading edges of pulses passed by data gate 26. After being so triggered, it produces an output after a predetermined period of time, in this case two line scanning periods, or 127 microseconds. This output is connected to one input of an AND gate 36, the other input of which is connected to the output of window 31. Thus, an output from AND gate 36 is possible only if the timer has run and the analyzed X-ray event falls within the limits of the window.

The functioning of this delay circuit can be better appreciated by reference to FIGS. 3 and 4. In FIG. 3 two X-ray events, X, and X are shown, as they might occur during a portion of a scanning cycle. As a result of the delay in detecting and analyzing the X-ray events, it is seen that Y, and Y displays of X, and X respectively, are laterally displaced by substantial amounts and provide no useful correlation with the true position of the events. In FIG. 4, the displays Y, and Y have each been delayed by two horizontal scanning periods, or 127 microseconds, so that the displays fall immediately below their X-ray event. The resulting vertical spatial error, 2 lines in 525 lines, is less than 0.5 percent and can therefore be ignored.

The output of AND gate 36 is applied to a pulse forming circuit 37 wherein a pulse of predetermined amplitude and duration is generated for application to video processing circuits 21. A mode select or switch 38 is provided at the input of processing circuits 21 to permit the operator to select between a micrograph display mode and and X-ray area map mode. With the latter selection the X-ray events which have energy levels within the limits of window 31 will be displayed on the screen as momentary bright dots spatially aligned with their actual origin on the specimen as displayed in the micrograph mode. Since the dots appear at random throughout the display, it is contemplated that time lapse photography would be utilized in recording the X-ray area map. In practice, shutter openings of from 2 to 4 minutes have been employed. Because of the spatial correlations made possible by the invention, it is possible to superimpose an area map display on a micrograph by taking a double exposure; first of one, then of the other. It is also possible to generate a composite display by electronically combining the two signals with appropriate additive levels.

The SEM system output displays made possible by the invention can better be appreciated by reference to FIGS. 5 and 6. In FIG. 5 a micrograph is seen which displays five particles 39-43 greatly magnified. In FIG. 6, a time-lapse photographed X-ray area map is shown of the same five particles with the window adjusted to an energy level corresponding to one element, say titanium. Now only those particles composed of titanium, namely 39 and 42, appear. This indicates to the operator that titanium is present, and what the relative quantity and size of the titanium particles might be. It will be appreciated that by setting other window limits, other elements could be displayed instead, and that a simultaneous comparison is available with the histogram display to determine the energy level and relative concentration of the selected element.

In accordance with another aspect of the invention, a plurality of single channel windows is provided, the outputs of which can be simultaneously displayed in individual identifying colors on a single X-ray area map. Referring to FIG. 7, two single channel windows 44 and 45 are connected to the output of multiplexer 32. These channels simultaneously receive and process the applied digital address, although they would normally be adjusted to have different window centroids. The output of window 44 is connected to one input of AND gate 46, and the output of window 45 is connected to one input of an AND gate 47. The remaining inputs of AND gates 46 and 47 are connected to the output of display delay timer 35, and the outputs of gates 46 and 47 are connected to respective modulating signal inputs of a color modulator 48. A 3.58 MHz continuouswave color oscillator 49 is connected to the unmodulated signal input of modulator 48.

When the energy level of a pulse processed by analog to digital converter 27 falls within one of the two windows, an output is produced from that window. Then, when display delay timer 35 completes its cycle and provides an enabling output, the AND gate associated with the particular window provides an output pulse. This pulse is applied to color modulator 48, which responds by phase-modulating the 3.58 MHz signal from generator 49 to provide a color subcarrier to accompany the luminance signal. The phase of the subcarrier thus generated is individually adjustable for the two inputs, and may be made to change automatically as the energy centroid of the window is changed. Since the color of the X-ray area map ultimately displayed on the SEM system output monitor depends on the phase of the 3.58 MHz subcarrier, the output of each window can be displayed in a different color. Modulator 48 also includes a burst gate for periodically generating the reference burst required during each horizontal retrace interval by US. color television standards.

9 51. A mode switch 52 may be connected in series with the inputs of processing circuits 51 to provide either a micrograph display, a multi-color X-ray area map, or a composite micrograph and multi-color elemental area map. Video processing circuits 51 include necessary clamping and matrixing circuitry for combining the three input signals to form a composite signal suitable for application to one or more standard color monitors The effect of this arrangement can be seen in FIG. 8, which depicts a multi-color X-ray area map. in this case window 44 is set at 4510 electron-volts, which corresponds to titanium, and window 45 is set at 5410 electron-volts, which corresponds to the element chromium. Again, titanium particles 39 and 42 activate the 4,510 electron-volt window, but this time they produce a colored display, say green. Particles 40 and 41 activate the 5,410 electron-volt window, identifying themselves as chromium and being displayed in red. Particle 43, which is neither of these elements, would not be displayed in the X-ray area map display and would be displayed without color in the composite display.

The resulting display on monitor 57 comprises a histogram-type energy spectrum display similarto that shown in FIG. 9. By displaying the energy levels falling within a particular single channel window in the same color as in the X-ray area map display; e.g., green for the titanium peak 58 at 4,510 electron-volts and red for the chromium peak 59 at 5,410 electron-volts, correlation between the two displays is easily accomplished. As in the previously described monochrome display, the actual energy centroids of the single channel windows can be displayed in alphanumerics above the graphical data.

Thus, a noveltelevision display system for an electron microscope has been described which permits elemental identification by means of an X-ray area map spatially correlated to the micrographic output of the microscope. identification of the elemental energy level under analysis is also made on a simultaneously presented histogram-type energy spectral display to permit positive identification of the element and its relative composition in the specimen. A more advanced system has also been shown which permits simultaneous identification of multiple windows by color coding the electron microscope and energy distribution displays.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. in a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, a display system comprising:

a detector'for detecting said X-ray events and producing output pulses indicative of the energy level thereof;

means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their respective output pulses by random unpredictable time intervals;

correlation means responsive to said information sig nals for correlating said information signals with limits corresponding to a predetermined energy range and for producing a display pulse responsive to said correlation after a predetermined time interval following each of said respective output pulses;

a television monitor having a viewing screen scanned in synchronism with said specimen;

and means for applying said display pulses to said television monitor to obtain a spatially correlated X-ray area map display of said X-ray events.

2. A display system as defined in claim it wherein said correlation means comprise a single channel window circuit for producing a control effect when one of said information signals falls within said limits, and a timer responsive to said control effect for producing said display pulse after a predetermined delay period following the output pulse associated with said one information signal.

3. A display system as defined in claim 2 wherein said specimen is scanned in a line raster and said delay period comprises an integral number of line scanning periods.

4. A display system as defined in claim 2 wherein said electron microscope includes a detector for detecting secondary electrons and wherein means are provided for applying the output of said electron detector to said television monitor to display a micrograph of said specimen thereon in spatial correlation with said X-ray area map.

5. A display system as described in claim 2 wherein said display pulse includes a color subcarrier signal, said television monitor is a color video monitor and said spatially correlated display is a color display.

6. A display system as described in claim 1 wherein said information signals are digitally coded signals, and said correlation means include a digital window circuit for determining whether said coded signals fall within a predetermined energy range.

7. In a scanning elctron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, 2. display system comprising:

a detector for detecting said X-ray events and pro ducing output pulses indicative of the energy level thereof;

means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their associated events by random unpredictable time intervals;

a first single-channel window circuit for analyzing said information signals to produce a first control effect when one of said signals falls within limits corresponding to a first predetermined energy range;

a second single-channel window circuit for analyzing said information signals to produce a second control effect when one of said signals falls within limits corresponding to a second predetermined en ergy range;

means including a timer responsive to said first control effect for producing a first display pulse and responsive to said second control effect for produc ing a second display pulse, each of siad pulses being specimen is scanned in horizontal and vertical directions and said delay period comprises an integral number of horizontal scanning periods.

9. A display system as defined in claim 7 wherein said television monitor is a color monitor, and wherein said first display pulses appear on said monitor with a first distinguishing color, and said second display pulses ap pear on said monitor with a second distinguishing color.

10. In a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, a display system comprising:

a detector for detecting said X-ray events and producing output pulses indicative of the energy level thereof;

means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their associated events by random unpredictable time intervals;

a color television monitor;

an energy distribution analyzer for developing said television monitor from said information signals a histogram-type display of the energy levels of said X-ray events versus their cumulative occurrence over a period of time;

a first single channel window for analyzing said information signals to generate a first control effect when said signals fall within limits corresponding to a first predetermined energy range;

and means for varying the color of said histogram display to identify that portion of the display falling within said first predetermined energy range.

11. A display system as defined in claim 10 which further comprises a second single channel window for analyzing said information signals to generate a second control effect when said signals fall within limits corresponding to a second predetermined energy range, and means for futher varying the color of said histogram display to identify that portion of the display falling 

1. In a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, a display system comprising: a detector for detecting said X-ray events and producing output pulses indicative of the energy level thereof; means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their respective output pulses by random unpredictable time intervals; correlation means responsive to said information signals for correlating said information signals with limits corresponding to a predetermined energy range and for producing a display pulse responsive to said correlation after a predetermined time interval following each of said respective output pulses; a television monitor having a viewing screen scanned in synchronism with said specimen; and means for applying said display pulses to said television monitor to obtain a spatially correlated X-ray area map display of said X-ray events.
 2. A display system as defined in claim 1 wherein said correlation means comprise a single channel window circuit for producing a control effect when one of said information signals falls within said limits, and a timer responsive to said control effect for producing said display pulse after a predetermined delay period following the output pulse associated with said one information signal.
 3. A display system as defined in claim 2 wherein said specimen is scanned in a line raster and said delay period comprises an integral number of line scanning periods.
 4. A display system as defined in claim 2 wherein said electron microscope includes a detector for detecting secondary electrons and wherein means are provided for applying the output of said electron detector to said television monitor to display a micrograph of said specimen thereon in spatial correlation with said X-ray area map.
 5. A display system as described in claim 2 wherein said display pulse includes a color subcarrier signal, said television monitor is a color video monitor and said spatially correlated display is a color display.
 6. A display system as described in claim 1 wherein said information signals are digitally coded signals, and said correlation means include a digital window circuit for determining whether said coded signals fall within a predetermined energy range.
 7. In a scanning elctron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, a display system comprising: a detector for detecting said X-ray events and producing output pulses indicative of the energy level thereof; means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their associated events by random unpredictable time intervals; a first single-channel window circuit for analyzing said information signals to produce a first control effect when one of said signals falls within limits corresponding to a first predetermined energy range; a second single-channel window circuit for analyzing said information signals to produce a second control effect when one of said signals falls within limits corresponding to a second predetermined energy range; means including a timer responsive to said first control effect for producing a first display pulse and responsive to said second control effect for producing a second display pulse, each of siad pulses being produced after a predetermined delay period fOllowing the X-ray event associated with the respective control effect; a television monitor having a viewing screen scanned in synchronism with said specimen; and means for applying said first and second display pulses to said television monitor to obtain a spatially correlated display of said X-ray events having energy levels within said first and second predetermined energy ranges.
 8. A display system as defined in claim 7 wherein said specimen is scanned in horizontal and vertical directions and said delay period comprises an integral number of horizontal scanning periods.
 9. A display system as defined in claim 7 wherein said television monitor is a color monitor, and wherein said first display pulses appear on said monitor with a first distinguishing color, and said second display pulses appear on said monitor with a second distinguishing color.
 10. In a scanning electron microscope of the type wherein a series of X-ray emission events are produced as a specimen is cyclically scanned by an electron beam, a display system comprising: a detector for detecting said X-ray events and producing output pulses indicative of the energy level thereof; means for converting at least some of said output pulses to energy-indicative information signals, said information signals following their associated events by random unpredictable time intervals; a color television monitor; an energy distribution analyzer for developing said television monitor from said information signals a histogram-type display of the energy levels of said X-ray events versus their cumulative occurrence over a period of time; a first single channel window for analyzing said information signals to generate a first control effect when said signals fall within limits corresponding to a first predetermined energy range; and means for varying the color of said histogram display to identify that portion of the display falling within said first predetermined energy range.
 11. A display system as defined in claim 10 which further comprises a second single channel window for analyzing said information signals to generate a second control effect when said signals fall within limits corresponding to a second predetermined energy range, and means for futher varying the color of said histogram display to identify that portion of the display falling within said second predetermined energy range. 